We are continuing our investigation of the genetic control of the cell cycle of yeast. Emphasis in the coming year will be in three areas: (1) Genetic control of 2 micron DNA replication. The yeast 2 micron circular DNA plasmid may be a useful model for DNA replication in yeast. We will try to determine whether its replication depends upon the same genes that are necessary for nuclear DNA initiation and replication, whether a copy is integrated into the nuclear genome and to study the inheritance of altered forms of the plasmid. (2) Control of cell division by mating factor. The yeast mating factor is a small polypeptide that controls cell division at a specific point in G1. We have purified factor and will study its metabolism and interaction with cellular components in wild type and mating factor resistant mutants in an attempt to learn its mode of action. (3) Sequential gene function during the cell cycle. We will study the effects of Benomyl (a purported mitotic arrest agent) upon the yeast cell cycle and determine which cdc gene functions are dependent for their activity upon completion of the Benomyl sensitive step and vice versa.